Communication devices such as terminals are also known as e.g. User Equipments (UE), mobile terminals, wireless devices, wireless terminals and/or mobile stations. Terminals are enabled to communicate wirelessly in a wireless communications network such as a cellular communications network, sometimes also referred to as a cellular radio system or cellular networks. The communication may be performed e.g. between two terminals, between a terminal and a regular telephone and/or between a terminal and a server via a Radio Access Network (RAN) and possibly one or more core networks, comprised within the cellular communications network.
Terminals may further be referred to as mobile telephones, cellular telephones, laptops, or surf plates with wireless capability, just to mention some further examples. The terminals in the present context may be, for example, portable, pocket-storable, hand-held, computer-comprised, or vehicle-mounted mobile devices, enabled to communicate voice and/or data, via the RAN, with another entity, such as another terminal or a server.
The cellular communications network covers a geographical area which is divided into cell areas, wherein each cell area being served by an access node such as a base station, e.g. a Radio Base Station (RBS), which sometimes may be referred to as e.g. “eNB”, “eNodeB”, “NodeB”, “B node”, or BTS (Base Transceiver Station), depending on the technology and terminology used. The base stations may be of different classes such as e.g. macro eNodeB, home eNodeB or pico base station, based on transmission power and thereby also cell size. A cell is the geographical area where radio coverage is provided by the base station at a base station site. One base station, situated on the base station site, may serve one or several cells. Further, each base station may support one or several communication technologies. The base stations communicate over the air interface operating on radio frequencies with the terminals within range of the base stations. In the context of this disclosure, the expression Downlink (DL) is used for the transmission path from the base station to the mobile station. The expression Uplink (UL) is used for the transmission path in the opposite direction i.e. from the mobile station to the base station.
In 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE), base stations, which may be referred to as eNodeBs or even eNBs, may be directly connected to one or more core networks.
3GPP LTE radio access standard has been written in order to support high bitrates and low latency both for uplink and downlink traffic. All data transmission is in LTE controlled by the radio base station.
The Institute of Electrical and Electronics Engineers (IEEE) 802.11 standard that defines the physical (PHY) layer and Media Access Control (MAC) layer for Wireless Local Area Networks (WLANs) specifies several different channel access mechanisms, such as the Distributed Coordination Function (DCF), the Point Coordination Function (PCF), and some variants of the Hybrid Coordination Function (HCF), etc.
The DCF is a MAC technique and requires a wireless device wishing to transmit to listen for the RF channel status for a Distributed (coordination function) lnterframe Space (DIFS) interval. If the RF channel is found busy during the DIFS interval, the wireless device defers its transmission. In a wireless communications network, wherein a number of wireless devices contend for the wireless medium, if multiple wireless devices sense that the channel is busy and defer their access, they will also virtually simultaneously find that the RF channel is released and then try to seize the channel. As a result, collisions may occur. In order to avoid such collisions, DCF also specifies random back off, which forces a wireless device to defer its access to the RF channel for an extra period of time.
The PCF is also a MAC technique and it resides in a point coordinator, such as an Access Point (AP), in order to coordinate the communication within the wireless communications network. The AP waits for a Point (coordination function) lnterframe Space (PIFS) duration rather than the DIFS duration before it tries to access the RF channel. The PIFS duration is less than the DIFS duration and hence the point coordinator, e.g. the AP, has a higher priority to access the RF channel than the wireless devices.
The IEEE 802.11e standard enhances the DCF and the PCF, through a new coordination function: the Hybrid Coordination Function (HCF). HCF combines functions from the DCF and PCF with some enhanced Quality of Service (QoS) specific mechanisms and frame subtypes to allow a uniform set of frame exchange sequences to be used for QoS data transfers. Within the HCF, there are two methods of channel access, similar to those defined in the legacy IEEE 802.11 MAC: HCF Controlled Channel Access (HCCA) and Enhanced Distributed Channel Access (EDCA). Both EDCA and HCCA define Traffic Categories (TC).
Even though the DCF, PCF, and HCF mechanisms mentioned above have been proposed and standardized by the IEEE, in practice virtually all current WLAN, sometimes herein also referred to as Wi-Fi, deployments are based on the DCF. The DCF, which is based on Carrier Sensing Multiple Access with Collision Avoidance (CSMA/CA), has achieved its popularity due to e.g. its robustness. CSMA/CA is a network multiple access method in which so called carrier sensing is used, but the nodes attempt to avoid collisions by transmitting only when the channel is sensed to be “idle”. However, there are several drawbacks associated with the DCF. For example, some drawbacks are the uplink and/or downlink throughput imbalance as well as the imbalance between different wireless communications networks operating on the same Radio Frequency (RF) channel.
Thus, the state of the art WLANs are associated with some drawbacks such as the uplink and/or downlink throughput imbalance as well as the imbalance between different wireless communications networks operating on the same RF channel.